Bounds of biodiversity

LTER scientists to seek out life in Transantarctic Mountains

Scientists who normally spend much of the austral summer in the McMurdo Dry Valleys conducting long-term studies on that polar desert ecosystem are taking their research on the road.

Byron Adams, an associate professor of biology at Brigham Young University, will lead a small team of colleagues on a series of short excursions to the Beardmore Glacier in the Transantarctic Mountains this year. The project is something of a reconnaissance mission to determine if viable communities of microorganisms inhabit the exposed soils in a high and dry area dominated by ice.

“We’re really interested about the biodiversity of these organisms that are there, and we’re particularly interested in their evolutionary history as well,” explained Adams, a member of the McMurdo Dry Valleys Long Term Ecological Research (LTER) program, a multidisciplinary study of the lakes and soils in Antarctica’s largest ice-free region.

The soil-dwelling organisms of the McMurdo Dry Valleys — such as the tardigrade and wormy nematodes — are found throughout the world. However, many of the Antarctic species are endemic, implying a long, unbroken evolutionary history.

That’s the story that Adams can read in the molecular structures of the animals, particularly nematodes, when compared to their distant cousins on other southern hemisphere continents.

Ice block

There’s just one problem, Adams said. The models used by glaciologists to represent the extent of the Antarctic ice sheet in the past covers all the areas where these animals inhabit. That means all the different tardigrades, nematodes and other metazoans that Adams and his colleagues in the McMurdo Dry Valleys LTER study only colonized the region within the last 20,000 years after the ice last reached its maximum extent.

“That model leaves no room for any refugia for any of these animals to persist, therefore these areas must have been completely devoid of organisms that later re-colonized these areas,” said Adams. But the geographic distribution and diversity of today’s tiny critters indicate an evolutionary history on a much greater time scale.

“Biology is telling us a different story than the models the glaciologists have come up with,” Adams said. “We’re arguing that these organisms survived the Pleistocene glaciation somewhere in Antarctica.”

Adams believes that in high-altitude areas the microorganisms found refuge from the repeated thrust and retreat of the ice sheet that marked the 2.5 million years of the Pleistocene, which ended about 12,000 years ago with the onset of the relatively warm and stable Holocene. In un-glaciated places like Mount Seuss, an elevated area in the Dry Valleys, scientists have found high genetic diversity among the animals, he added.

“The populations that persisted there seeded these other areas that opened up” after the ice sheet retreated, he explained. “[The] most compelling evidence is that in 15,000 years, 12,000 years, even 20,000 years, you just can’t produce the diversity of species we have on continental Antarctica. You just can’t do that in that short period of time.”

New territory

Adams hopes to add more evidence to support that theory if his team can find similar diversity in the exposed soils in the Beardmore region. “We would predict that these organisms in these isolated populations would respond in concert to the climate changes, the environmental changes that are imposed on them. Using tools of molecular evolution, we can do these types of comparisons,” he said.

While there have been few biological studies in the mountains, Adams said researchers do know life exists in isolated pockets far from the Dry Valleys. In fact, he was the lead author of a paper published a couple of years ago in Polar Biology that described the discovery of the southernmost nematode, Scottnema lindsayae, which New Zealand colleague Ian Hogg brought back from the mouth of the Beardmore Glacier. Hogg is also a member of the team headed to the Beardmore region this year.

“We’ll probably be some of the first biologists to collect in some of these areas,” Adams noted. “It’s like going to Mars or the moon for us. It’s a place where biologists really haven’t been.”

Documenting distribution

Diana Wall, a soil biologist from Colorado State University and co-principal investigator on the project, said it is important for the team to document the distribution of species outside the Dry Valleys to gauge their resilience to climate change.

“One of the things we need to know with climate change is how big the climate envelope is for a particular species,” explained Wall, entering her 20th season working in the Dry Valleys. “To know that kind of thing, we need to know the range of the different species.”

For example, in collaboration with the New Zealand science program, scientists ventured as far north at Cape Hallet, about 400 kilometers from the northern edge of the Dry Valleys. An algae-feeding nematode at the more northerly location differed from one found in the Dry Valleys, Wall said.

Climate change

Most climate change studies in Antarctica focus on the western ice sheet. If anything, the long-term trend in the McMurdo Dry Valleys, right on the edge of East Antarctica, has been slight cooling. However, a series of short-term flooding events in recent years has illustrated how quickly the system can respond to even minor changes.

“If you turn that temperature gauge half a degree above freezing for a period of time, you generate a lot of water,” noted Berry Lyons, who is also on the McMurdo LTER and is a geochemist from The Byrd Polar Research Center at The Ohio State University.

“I think these are extremely sensitive systems, and slight increases in temperature in summer time really have a profound effect on how much water you generate,” added Lyons, who is also a co-principal investigator on the Beardmore team. His role will be to support the biological study by analyzing the geochemistry of the soils.

“The chemistry is just an aid to better understand the habitat — the soil’s age and composition, how much nitrogen and carbon and how much salt,” he explained. “I think they’re probably going to look like a lot of the higher elevation soils we see in the Dry Valleys.”

Going high and dry

That’s different from the floor of the Valleys, where moisture from streams, lakes and permafrost melt helps drive the activity, productivity and density of the organisms in the soil. Wall’s “worm herders” science team has found nematodes in up to 70 percent of the Dry Valley soils.

In extremely dry soil areas, she said, only the nematode Scottnema lindsayae has the temerity to survive, remaining in an anhydrobiotic state, a sort of stasis where all metabolic activities cease and it loses up to 99 percent of its water content until moisture is available. It can remain that way indefinitely.

“It’s the Rambo [of nematodes]. It’s a tough worm,” Wall noted.

Added Adams, “We can find old soils that are dry and have these nematodes in them. We can add water to them and they come alive. We still don’t know the answer to the question about how old these things are and how long they can live in this state.”